Terpolymer production

Abstract

Terpolymers comprising propylene and small amounts of ethylene and butene-1 are made in a two-stage process wherein a relatively high melting random terpolymer is made in a first stage and a relatively low-melting random terpolymer incorporating a higher concentration of ethylene, is made in a second stage so that it is dispersed in the product of the first stage. The two process stages may be operated in a single batch reactor or two continuous reactors in series.

We claim: 
     
       1. Method of making a modified polypropylene in hexane slurry, said polypropylene having improved low-temperature thermal properties comprising (a) maintaining in a first stage under polymerizing conditions, including a pressure of about 140 psig to about 160 psig, a hexane-catalyst slurry in equilibrium with a gas phase composition comprising about 93.9% propylene, about 4.65% to about 5.15% 1-butene, and about 1.14% to about 1.26% ethylene, to form a dispersion in said slurry of terpolymer particles, and (b) then imposing on said slurry of terpolymer particles, under polymerizing conditions in a second stage, a concentration of ethylene in the gas phase increased to about 2% to about 4%, thereby forming a substrate terpolymer including about 3% to about 4% ethylene and about 3% to about 5.6% 1-butene, and recovering a polymer product having a melting point of about 130° C. to about 140° C. 
     
     
       2. Method of claim 1 wherein the concentrations of monomers in step (a) are maintained in the slurry by maintaining the reaction vessel at a pressure of from about 140 psig to about 160 psig. 
     
     
       3. Method of claim 1 wherein the second stage of the process is conducted in a reaction vessel different from the first stage. 
     
     
       4. Method of claim 1 wherein no 1-butene is fed to the second stage. 
     
     
       5. Method of claim 1 including the step of recovering a polymer product having a melting point of about 130° C. to about 140° C. 
     
     
       6. Method of claim 1 wherein the gas cap concentration of ethylene in the second step is maintained at about 3.23% to about 3.57%.